In recent years, an augmented reality (AR) technique has attracted attention, in which a virtual object or a variety of information as additional information is combined with a real environment (or a portion thereof), and the combined result is presented as electronic information. In order to realize this augmented reality technique, for example, a head mounted display has been examined as an instrument for presenting visual information. In addition, examples of application fields include provision of route guidance information and provision of technique information to an engineer who performs maintenance, which are expected to support the work in a real environment. Particularly, the head mounted display is very convenient since the hands are free. In addition, in a case where videos or images are desired to be enjoyed while moving outdoors as well, the videos or the images and the external environment can be understood simultaneously in the range of vision, and thus smooth movement is possible.
For example, JP-A-2006-162767 discloses a virtual image display apparatus (image display apparatus) which causes a two-dimensional image formed by an image forming device to be observed by an observer as an enlarged virtual image using a virtual image optical system.
As shown in FIG. 29 which is a conceptual diagram, the image display apparatus 100′ includes an image forming device 111 provided with a plurality of pixels arranged in a two-dimensional matrix state, a collimating optical system 112 which converts light emitted from the pixels of the image forming device 111 into parallel light, and an optical device (light guide unit) 120 which guides and emits incident light which has been converted into the parallel light in the collimating optical system 112. The optical device 120 includes a light guide plate 121 which causes the incident light to propagate through total reflection and to be emitted, a first deflection unit 130 (for example, formed of a single-layer light reflection film) which reflects the light incident to the light guide plate 121 such that the light incident to the light guide plate 121 is totally reflected inside the light guide plate 121, and a second deflection unit 140 (for example, formed of multi-layer light reflection films having a multi-layer laminate structure) which emits the light which has propagated inside the light guide plate 121 through the total reflection, from the light guide plate 121. In addition, if, for example, an HMD is formed using the image display apparatus 100′, it is possible to achieve light weight and miniaturization of the apparatus. In addition, an image display apparatus according to Embodiment 1 described with reference to FIG. 1 is referred to in relation to the reference numerals indicating other constituent elements in FIG. 29.
Alternatively, for example, JP-A-2007-94175 discloses a virtual image display apparatus (image display apparatus) which employs a hologram diffraction grating in order to cause a two-dimensional image formed by an image forming device to be observed by an observer as an enlarged virtual image using a virtual image optical system.
As shown in FIG. 30 which is a conceptual diagram, the image display apparatus 300′ basically includes an image forming device 111 which displays an image, a collimating optical system 112, and an optical device (light guide unit) 320 to which light displayed in the image forming device 111 is incident and which guides the light to the pupil 21 of the observer. Here, the optical device 320 includes a light guide plate 321, and a first diffraction grating member 330 and a second diffraction grating member 340 formed by a reflective volume hologram diffraction grating provided in the light guide plate 321. In addition, light emitted from each pixel of the image forming device 111 is incident to the collimating optical system 112, and thus a plurality of parallel light beams of which angles incident to the light guide plate 321 are different are generated by the collimating optical system 112 and are incident to the light guide plate 321. The incident parallel light beams are emitted from a first surface 322 of the light guide plate 321. On the other hand, the first diffraction grating member 330 and the second diffraction grating member 340 are installed on a second surface 323 of the light guide plate 321, parallel to the first surface 322 of the light guide plate 321. In addition, an image display apparatus according to Embodiment 3 described with reference to FIG. 13 is referred to in relation to the reference numerals indicating other constituent elements in FIG. 30.
In addition, an image is displayed on the image display apparatus 100′ or 300′, and thereby an observer can observe an external object and the displayed image in an overlapping manner. In addition, for convenience, these image display apparatuses 100′ and 300′ are referred to as “semi-transmissive image display apparatuses”.
On the other hand, for example, JP-A-2008-103916 discloses an image display apparatus of a type different from that of the above-described image display apparatuses. In the image display apparatus disclosed therein, an observer can observe an image, displayed in the image display apparatus, related to the augmented reality technique but is unable to observe an external object. In addition, for convenience, this image display apparatus is referred to as a “non-transmissive image display apparatus”.